1. Field of the Invention
The present invention relates to a method of manufacturing electric devices and, more particularly to a method of manufacturing electric device utilizing crystalline films such as diamond light emitting devices.
2. Description of the Prior Art
There have been many electric devices utilizing thin film semiconductors. The manufacturing methods of such devices require suitable measures to overcome peculiar problems originating from film semiconductors.
For emission of reddish light rays, GaAs semiconductors have been utilized to manufacture light emitting devices for more than a decade. The emission of blue or green light, as well as white light, however, has long been hardly realized by means of solid state devices.
The inventor has before proposed to make a light emitting device from a diamond film which can emit light at short wave lengths, for example, as described in Japanese Patent Application No sho 56-146930 filed on Sep. 17, 1981. Diamond is promising, as a light emitting substance for mass production, because of its high thermal resistance, chemically stabilities and low price, in view of a great demand for light emitting devices in the market. It is, however, very difficult to manufacture diamond light emitting devices at a high yield required for commercialization because there are formed a large proportion of products whose efficiencies are undesirably too low to satisfy the requirement of the application thereof. Furthermore, the performance of prior art diamond devices tend to quickly age by actual operation. For example, prior art diamond light emitting devices were heated up to 50.degree. C. only by application of 30 V for 10 min. and the performances were then significantly degraded.
The light emitting action of diamond light emitting devices takes place when a relatively large current is passed through diamond crystals by applying a voltage between a pair of electrodes sandwiching the diamond crystals. The electric energy carried by the current, however, is consumed largely only to produce heat rather than to emit light rays. The inventor successed in the discovery of the origin of the low efficiencies and the heat generation. As a result, the following fact has been found.
When deposited, diamond tends to form a polycrystalline film 2 composed of columnar crystals 2 grown at right angles on a substrate as illustrated in FIG. 1. There are formed many grain boundaries 4 extending through the diamond film 2. It was found by Raman spectroscopic analysis that these grain boundaries consists of segregation of carbon graphite (having sp.sup.2 bonds) which has a resistivity substantially lower than that of diamond crystals (having sp.sup.3 bonds), e.g. by a factor of 10.sup.2 .about.10.sup.4. Furthermore, these boundaries tend to gather impurities such as metallic ions occurring inadvertently in the film 2 or introduced intentionally into diamond films particularly during thermal treatment. The metallic ions or other impurities also function to elevate the conductivity of the boundaries. Because of this, a large proportion of current flows across the film along the boundaries rather than through the diamond crystals. It is for this reason that prior art diamond electric devices can not exhibit sufficient performances which are inherently expected from the characteristics of diamond itself. For example, the current passing through the boundaries has no contribution to light emitting but only function to generate heat. Another origin of heat generation is existence of pinholes 5 passing through the film 2 which are undesirably but often formed during deposition. When an upper electrode 3 is deposited, short current passages are formed undesirably. Similar drawbacks commonly exist in other crystalline films.